A federal law enforcement official added that Ciancia “wasn’t a fan of the TSA.”

Leon Saryan of Greenfield, Wisc., told Mikwaukee radio station WTMJ that he was approached by the gunman.

“He looked at me and he said 'TSA?' and I shook my head and he just kept going," he said.

Authorities believe that Ciancia arrived at a TSA screening area in Terminal 3 at 9:20 a.m., pulled a rifle out of his bag and started shooting. He made his way past the security checkpoint into the terminal and continued shooting.

[Updated at 4:20 p.m.: Stephanie Rosemeyer, 26 was in Terminal 3 Friday morning waiting to board a flight to Chicago when she heard airport alarms go off and saw people suddenly start running toward the exits.

At first, she thought a plane had crashed or a fire had broken out. But when she left her seat at Gate 36 to go look, she saw people huddled in the nearby food court. She also saw a man carrying a gun, dressed in all black and wearing a bulletproof vest. He was alone and didn't appear to be law enforcement.

Her gaze met the gunman’s, she said. She gave him a “quizzical” look.

“He looked back at me, and said ‘I don’t like this,’" she said. "I took a step toward him" and he shouted an expletive directed at the TSA.

“I decided to walk away, and then I heard gun shots, and so I walked faster,” she said.

She heard at least five gunshots as the shooter continued to shout about the TSA. She slid behind a wall and moved toward the exit doors at the back of the terminal. She didn’t see anyone get shot, but as she hustled down the stairs she said she heard more gunshots.]

The suspect was eventually shot by authorities elsewhere in the terminal. He was in critical condition.

The attack caused widespread chaos at the airport, with flights delayed and thousand of passengers left stranded on the streets in and around the airport.

Authorities said the gunman fired at several locations in Terminal 3 before police shot him.

The motive for the shooting was unclear. A federal law enforcement official said the gunman was a ticketed passenger entering the airport. Los Angeles Police Department anti-terrorism officials were on the scene, but sources said they believed the suspect acted alone and was not tied to any known terrorist group.

At a news conference, the Los Angeles Fire Departmentsaid it treated seven people at the scene and transported six to local hospitals. The TSA said "multiple" agents were hurt in the incident.

At Ronald Reagan UCLA Medical Center, Dr. Lynne McCullough told reporters that the hospital was treating three adult males. One was in critical condition with multiple gunshot wounds, she said, and another was in fair condition with gunshot wounds. The third victim was in fair condition with unspecified injuries.

The gunshot wounds were in "a variety of areas" of their bodies, McCullough said.

"Our hearts go out to the families" of the victims, McCullough said.

Patrick Gannon, the LAX police chief, said the gunman entered Terminal 3 at 9:20 a.m., pulled an assault rifle out of his bag and began firing. He moved into the screening area and continued shooting, Gannon said. He got past the checkpoint and moved further into the terminal.

Authorities tracked him down and shot him near a Burger King.

Vernon Cardenas, 45, of West Hollywood said he was at the airport on his way to Philadelphia when the shooting occurred about 9:30 a.m.

“Sitting down, all of a sudden, literally just out of the blue, you hear a rumble in the background, and a couple of seconds later people are running at me,” said Cardenas, who does casting for the Fox television show "MasterChef." He described the scene as “mayhem,” with couples crying and parents who couldn’t find their children.

Brian Adamick, 43, said he was boarding a Spirit Airlines flight to Chicago at Gate 32 when a commotion erupted.

He said people were running through the terminal, away from a security area. Adamick said he went through an emergency exit downstairs onto the tarmac with several other passengers.

“While I was on the tarmac, I heard two gunshots from the same area where the people had been running and screaming,” he said.

A few minutes after he got outside, he said buses showed up to help evacuate passengers. He said he saw a wounded TSA agent board one of the buses. The man’s ankle was bloody: “It looked like it was straight out of the movies,” Adamick said.

The man told him, “I got shot, I’m fine.” He told passengers not to worry about him and that he had been shot before, Adamick said.

A White House official said President Obama had been informed of the incident: "The president has been briefed about the shooting at LAX. We will continue to stay in touch with our federal and local partners. The LAPD is leading the response and investigation. We urge citizens to listen to the authorities and follow directions from the first responders on site. The president will continue to receive briefings throughout the day.”

Tory Belleci of the television show "Mythbusters" tweeted: "Heard gun shots then everyone starting running for the door. Not sure if anyone was hurt. #LAX."

TV news footage showed dozens of officers swarming the airport. Images also showed a law enforcement officer being treated by paramedics. He appeared to be alert. Another officer had a bloody hand.